docs: add collections usage

[lmeyerov]

Summary

• clarify collections purpose in the notebook intro and add a layered-highlights callout in 10min
• rebalance layout settings with lighter collections guidance and an encodings pointer
• move collections wire-protocol details into the spec and keep examples focused

RTD Preview

• demos/more_examples/graphistry_features/collections.ipynb: https://pygraphistry--875.org.readthedocs.build/en/875/demos/more_examples/graphistry_features/collections.html
• docs/source/10min.rst: https://pygraphistry--875.org.readthedocs.build/en/875/10min.html
• docs/source/cheatsheet.md: https://pygraphistry--875.org.readthedocs.build/en/875/cheatsheet.html
• docs/source/gfql/quick.rst: https://pygraphistry--875.org.readthedocs.build/en/875/gfql/quick.html
• docs/source/gfql/remote.rst: https://pygraphistry--875.org.readthedocs.build/en/875/gfql/remote.html
• docs/source/gfql/spec/wire_protocol.md: https://pygraphistry--875.org.readthedocs.build/en/875/gfql/spec/wire_protocol.html
• docs/source/gfql/wire_protocol_examples.md: https://pygraphistry--875.org.readthedocs.build/en/875/gfql/wire_protocol_examples.html
• docs/source/notebooks/visualization.rst: https://pygraphistry--875.org.readthedocs.build/en/875/notebooks/visualization.html
• docs/source/visualization/10min.rst: https://pygraphistry--875.org.readthedocs.build/en/875/visualization/10min.html
• docs/source/visualization/index.rst: https://pygraphistry--875.org.readthedocs.build/en/875/visualization/index.html
• docs/source/visualization/layout/settings.rst: https://pygraphistry--875.org.readthedocs.build/en/875/visualization/layout/settings.html

Testing

• not run (docs only)